These resemble neon lamps, but have a white phosphor coated onto the inside
surface of the bulb. This phosphor glows green, blue, white or some
kind of "warm white".

One version of this is the NE-2G, which is about the size of an NE-2H lamp,
about 3/4 inch (19 mm.) long by about a quarter inch (6.3 mm.) in
diameter. It is filled with a mixture of neon and xenon gases. Since the
excited states of xenon have lower energy levels than those of neon, almost
no neon atoms are excited. The glow discharge radiates almost entirely xenon
radiation, including a very short wavelength UV that excites the green-glowing
phosphor.

I recommend a series resistor of at least 56K with the NE-2G for use with 120
volts AC, at least 120K for use with 220 volts AC, and at least 150K for use with
240 volts AC. It may be a good idea to use a somewhat higher value resistor to
prolong the life of the phosphor.

A similar but smaller bulb with a neon-krypton mixture is found in Radio Shack's
272-708 green "neon" lamp cartridge. This is not as bright as the NE-2G. If you
can identify the resistor inside the cartridge (I have seen 56K and 100K ones
here), I recommend adding a resistor in series to get a total resistance of
110K to get a good life expectancy.

The NE-2G is about half as bright as an NE-2H with equal current. This makes an
NE-2G about a third as bright as an NE-2H since the NE-2H can take about 50
percent more current and still have a very long life. However, for night light
applications, the green "neon" lamps have a possible advantage: night vision
(scotopic vision) is very sensitive to the green light, much more so than to
an equal number of "lumens" of red, orange, yellow, or incandescent light or even
the yellow-green light of most green LEDs. Once you are dark-adapted,
you may find one green "neon" lamp to easily illuminate one or two large rooms
enough to find your way around in the dark.

There are white neon lamps also. One is available from Jameco
(http://www.jameco.com/) with a
catalog number of 146202. This lamp has a white phosphor like that of
4100K triphosphor fluorescent lamps and a neon-xenon mixture. The color of
the emitted light is an orangish white.

UPDATE 1/28/2000 Some lamps like these have a mixture of mercury vapor and
argon (or maybe another noble gas). I recently got a sample of a green
nightlight used in Europe. It's spectrum shows mercury. It also does not
reliably work at all at 120 volts AC and such lamps may only be widely
used where the line voltage is 220-240 volts AC.

Spectrum tubes are basically short "neon" tubing. The more popular "Plucker"
tubes can be found in some high school and college science labs. These are
about a foot (30 cm) long. The central portion is about a third of this length
and is quite narrow, about 6 mm. (1/4 inch) in outside diameter and one or two
millimeters inside diameter. The end portions are about a half inch (13 or so
mm.) in diameter and resemble those of "neon" tubing. These tubes come with any
of several gases and vapors, and are used with a spectroscope to demonstrate
the spectra of these gases.

Similar are "Geissler tubes", which have larger, sometimes coiled central
portions.

The Plucker tubes require a few thousand volts with current limited to a few
milliamps. Special power supplies for these are available, but generally
expensive. An alternative is a neon sign transformer with a reduced voltage
(about a quarter to half of normal) applied to its primary. These tubes also
usually work well with Tesla coils. It is generally recommended to not have
the average current exceed about 5 or 10 milliamps or so. Peak currents should
generally be kept under 100 mA, preferably under 40 mA to minimize sputtering
of the electrodes.

Extreme peak currents of many amps will make many of these gases glow a light
blue or blue-white color, but the electrodes were not designed to make these
tubes work as flashtubes. Any attempt at "flashtube" operation should be done
sparingly and with low energy levels, preferably well under a joule.

Tubes containing hydrogen, helium, neon, argon, krypton, xenon, and mercury vapor
(probably combined with one of the noble gases) are suitable for extensive
experimental and demonstration use. Tubes with other gases (especially air,
oxygen, water vapor, or ESPECIALLY any of the halogens) are more prone to internal
corrosion and should be used sparingly and not expected to have a good life
expectancy. The neon tube is the brightest of these and costs about 15, maybe
26 US$ as of about 2000. These tubes are available at Edmund Scientific
(1-609-573-6250) and some other scientific equipment suppliers.

Typical colors associated with various gases:

Hydrogen - Lavendar at low current, hot pinkish magenta if the peak current is
near or over 10 mA.
Helium - Whitish orange. Has been reported to be grayish, bluish, or green-bluish
white under some conditions, but I have not seen this.
Neon - Red-orange.
Argon - Violetish lavendar. Bright light blue at extreme peak currents.
Nitrogen - Similar to argon, slightly duller and often slightly more pinkish.
Bright bluish white, usually whiter than argon, at extreme peak currents.
Oxygen - Violet-lavendar, dimmer than argon.
Krypton - Grayish dim off-white, may have some greenish tint. Bright blue-white
at extreme peak currents. (I have not seen this gas glowing in this tube, but
I have seen krypton glowing elsewhere.)
Mercury Vapor - Light blue.
Xenon - Grayish or blue-grayish dim white. Very bright green-bluish white at
extreme peak currents, more green-blue in this tube than is typical of most
flashtubes.
Water Vapor - Similar to hydrogen but dimmer.
Carbon Dioxide - Slightly bluish white, brighter than xenon unless peak current
is really high.

An electroluminescent lamp is basically a capacitor with a "lossy" dielectric
that includes some sort of phosphor to make light from part of the
dielectric loss. They must have AC, or at least very unsteady DC, in order to
work. These typically require somewhat high voltages. A minimum of something
like 20 volts or so is needed to make them work, and these typically use
100-140 volts AC, up to 200 volts if the waveform is a square wave. At
power line frequencies of 50-60 Hz, electroluminescent lamps are not
bright, but last several years. To get more brightness, AC of higher
frequencies of a few hundred Hz (possibly even a few KHz?) is needed.

The "Lime Light" is an electroluminescent night light that has an
appearance something like a miniaturized TV set (with no controls,
speaker, antenna, etc). It consumes some very small amount of power (I
forget exactly) like about 1/16 watt. The screen glows with a slightly
whitish, maybe slightly bluish shade of green roughly like that of many
green traffic lights. The light output is a bit more than that of NE-2G
green neon lamps, easily enough to illuminate even a large room or two for
night vision. The luminous efficiency is comparable to that of
incandescent lamps, although much higher for night vision.

"Californeon" is a name for flexible electroluminescent strips that can be
worn by cyclists, joggers, Trick-or-treaters, partyers, etc. These come
with an inverter that produces the necessary high voltage higher frequency
AC from batteries. I believe these are the bright, slightly whitish green
things I have seen before.

For more info on the web for "Californeon", go to Altavista (http://www.altavista.com)
and do a simple search on californeon. You will get about a hundred
hits including some places that sell this stuff.

Some LCD computer screens used in laptop computers have electroluminescent
backlights. These usually glow with a color roughly like that of a "cool
white" fluorescent lamp. An inverter is used to supply AC with a voltage
around 100 volts or more and a frequency in the hundreds of Hz or maybe one
or two KHz. Some miniaturized TV sets also have electroluminescent
backlights. So do a few building entry intercoms and maybe other things
with LCD displays.

"Indiglo" is a brand name of smaller electroluminescent lighting devices used
in some watches and a nightlight and maybe a few calculators and the like.

Some smaller screens have LED backlights.

Many computer screens and maybe a few TVs have fluorescent backlights. If you
have a spectroscope, or even a diffraction grating or a CD to use as a
diffraction grating (requires practice), you can tell the difference.
Fluorescent lamps emit a spectrum containing mercury lines as well as the
spectrum of the phosphor (which varies). The mercury spectrum has significant
lines in the yellowish green and violetish blue, and weaker lines in the
yellow and deep violet. Phosphor spectra vary, sometimes basically continuous
and spanning most of the visible spectrum, sometimes consisting of bands. A
few phosphor bands have been known to be very narrow, resembling lines. Such
is the orange-red line/band found in the spectra of most compact fluorescent
lamps.

These are the first commercially successful variety of high efficiency red
LEDs, becoming widely available in the mid or late 1970's. Unlike the more
recent types of high efficiency red LEDs, these are efficient only at low
currents of a few milliamps or less. The brightness is noticeably less
than proportional to current as current increases above about 2 to 4
milliamps.

Low current red LEDs are made with gallium phosphide doped with zinc
oxide. Other gallium phosphide LEDs glow green or yellow-green.

The spectrum of low current red LEDs is broad, including the entire visible
red portion. Spec sheets often indicate a rather long peak wavelength around
690 nM, but this may be at low currents. The spectrum and color change with
current, and usually seems to be mostly red wavelengths shorter than 690 nM.
The color may be orange rather than red at currents around 20-30 mA, and the
different color does not alone indicate any damaging conditions or overheating
to the LED. When the color is orangish, a minor secondary spectral band
appears in the green around 550-560 nM.

Most other LEDs are most efficient at currents over 10 milliamps. However,
silicon carbide blue LEDs (without gallium nitride) are also most efficient
at low currents. Indium gallium nitride ultrabright green, blue and white LEDs
are also most efficient at lowish currents of a few milliamps.

In a few places, you might find what looks like neon tubing, but it is
dimmer and the color changes. The color typically cycles through some
sequence of different colors.

The tubing is actually a "light pipe", which is usually a solid rod of
transparent material or a bundle of optical fibers. Light that enters an
end of a transparent rod can totally reflect back into the rod every time
it hits the side, if its angle is more parallel to the axis of the rod
than some critical angle. The rod/"tubing" for the color changing "neon"
is slightly roughened, sanded, diffused, or otherwise made slightly "leaky".
The light entering the rod goes through (typically) some sort of mechanism
of colored filters, probably some sort of rotating wheel with different
color filter gels. The light source is, at least sometimes, a metal halide lamp.

There is another technology for color-changing neon tubing. The tubing in
this case is actual gas discharge tubing, and the waveform applied is
varied. The tubing has different ingredients. One waveform with a low peak
current favors one color, and another waveform with a high peak current
favors another color. For a little more info, check out:
http://www.multineon.com.

A neodymium bulb is an ordinary incandescent light bulb, except that the
bulb is made of a special bluish glass known as neodymium glass. Unlike
other light blue filter materials that slightly attenuate a broad range of
the spectrum from green through red, neodymium glass has a narrow
absorption band in the yellow and yellow-orange. A neodymium lamp glows
with a whiter color like that of some halogen lamps.

The special effect of the neodymium glass filtering is to achieve more red
and green output than usual for a light source of a given brightness and
overall color. This causes red and green objects to look slightly brighter
and more intensely colored than usual. The "triphosphor" type fluorescent
lamps, including most compact fluorescent lamps, have a similar effect
except that the fluorescents make bright pure reds look slightly orangish.

Neodymium bulbs are dimmer than unfiltered incandescent bulbs of the same
wattage and life expectancy. Neodymium bulbs do not have increased output
at any wavelength, except for an infrared band around 1064 nM where
neodymium glass fluoresces.

Neodymium bulbs are available as the General Electric "Enrich" and "Reveal"
bulbs At K-Mart and many other places where GE lightbulbs are sold.
Other neodymium bulbs including other wattages are available from a few
hardware stores, a few lighting/electrical supply shops and the like as
well as a few companies offering high-priced premium daylight-like light
sources, where the prices include hype including but not necessarily
limited to health claims. Bulbs.com
has a couple models. Major manufacturers include
Bulbrite and
Chromalux.

Tungar bulbs are gas filled low voltage, high current rectifier tubes. The
name refers to the fact that some are argon filled and have a tungsten
filament cathode. There are mercury vapor versions of these also. Tungar
bulbs were often used in car battery chargers before silicon diodes became
available. Tungar bulbs typically rectified a few amps and had peak
reverse voltage of a few tens of volts, and a forward voltage drop of
maybe around 10 volts.
The cathode typically required about 1.5 volts at around 15 amps. Some
mercury vapor models have more complex cathode structures that sometimes
trapped mercury, and the cathode drew even nore current for several
seconds to maybe a minute until the mercury was vaporized from the cathode
structure and the cathode reached normal operating temperature.

In operation with current flowing from cathode to anode, argon filled
models had a dim "fuzzball" of violetish colored glow around the filament.
At least in some models, the filament was so much brighter that the argon
glow was nearly invisible. Argon has a way of being unexpectedly dim at
currents around a few tenths of an amp to several amps. In mercury vapor
models, the glow is light blue and brighter. In at least one mercury model
with a more complex cathode structure and two anodes, the cathode has a
dim red-orange glow that is invisible through the brighter blue mercury
glow. The mercury glow also has a strange pattern, making this bulb
possibly useful for B-grade science fiction movies.

These light bulbs are most often approx. 3-1/8 inches (approx. 8 cm.) in
diameter, and have one of the following:
Two roses glowing pink or pink-orange and leaves that glow green.
A flamingo that glows pink or pink-orange and leaves that glow green.
Two orchids that glow dim violet with leaves that glow a brighter green.
Now there are other forms, but the three above are most common.

These lamps / bulbs are often known as "figural bulbs".

The birds/flowers are covered with a glow discharge like that of neon glow
lamps. The bulbs are filled with a gas mixture that is tailored to provide
some shortwave ultraviolet to cause a green-glowing phosphor on the leaves
to glow green.

Pink or pink-orange glow in these bulbs is achieved with a mixture of
neon, argon, and krypton but mostly neon. The neon-argon mixture is a
little more argon-rich than that optimized for easiest starting (maybe a
few percent argon). The argon adds some violet and violet-blue spectral
content to make the glow more pink and less orange. Some krypton is added to
add some visible blue-violet spectral content and some very-short-wave UV.

It is interesting to note that a 99.5 percent neon, .5 percent argon
mixture is popular in some neon lamps as a "Penning" mixture that ionizes
more easily than neon or argon alone. The cathode glow in these lamps is
orange, in fact more yellow than the color of pure neon. The "electron
temperature" is reduced, and the spectral output is shifted away from all
visible lines and towards the infrared argon lines. The violet and
violet-blue argon lines are extremely weak here. For some reason, the
strongest yellow line of neon is weakened less than other neon lines are,
making the neon color more yellow. In lamps with 99.5 percent neon, .5
percent argon and a main discharge column (such as many sodium lamps when
first started), the color is more magenta than that of pure neon.

In the bulb with violet orchids, the gas mixture is argon and xenon. The
visible spectral output is almost entirely that of argon, and the glow is
argon violet. The xenon produces very-short-wave UV. I have at times
seen the spectrum of barium from occaisional bright spots in the glow,
and believe the barium is a treatment to favor glow forming on
particular parts of the electrodes, or it may be a getter material.

The shortwave UV is very completely blocked by the glass bulb, and is not
any sort of hazard.

As for where to get these - Spencer
Gifts, at many malls - check your phone book or this link.

To some, there is no such thing as a medium pressure mercury vapor lamp. Any
mercury vapor lamp that is useful for anything would be either low pressure
(mercury vapor pressure of .000001 to .0002 atmosphere, usually plus some
inert gas) or high pressure (.05 atmosphere to hundreds of atmospheres).

However, there is a type of mercury vapor lamp usually called a medium
pressure mercury vapor lamp. The arc tube is quartz and anywhere from 5 to
as much as 77 inches (12 to 195 cm) long. The power input is high, typically 200
to 400 watts per inch of arc length, or 80 to 160 watts per centimeter of
arc length. The pressure is roughly 1/10 atmosphere to about an atmosphere.
So it can be said that this is a specialty type of high pressure mercury
vapor lamp.
The main feature of most "medium pressure" mercury vapor lamps is a higher
ratio of power input to amount of mercury vapor (in mass terms). Each
milligram of mercury vapor has to radiate more power - so the mercury vapor arc
achieves a somewhat higher temperature than is usual for high pressure mercury
vapor lamps. This improves ability to produce ultraviolet, especially at
wavelengths of 313 nm and shorter, in comparison to more ordinary high pressure
mercury vapor lamps.

These lamps are usually used in industrial applications requiring large
amounts of ultraviolet.

Please note that at close range, even if UV of wavelengths shorter than
365-366 nm is filtered out, the 365-366 nM UV may not be completely safe to
skin for prolonged exposure or for those taking photosensitizing prescription
drugs (ask your pharmacist). Large amounts of 365-366 nM UV are also not
completely safe for eyes.

Most fluorescent tubes are of the "hot cathode" type. In a hot cathode
fluorescent tube, the cathode is thermionically emissive and the typical
"cathode fall" (voltage drop to get an electron dislodged from metal and
into the gas discharge) is about 10 volts.

There are some oddball fluorescent lamps known as "cold cathode" fluorescent
lamps, which are lower current ones with non-thermionic electrodes and a
much higher cathode fall of over 50 volts.

The original cold cathode fluorescent lamps were basically slightly
oversized white "neon" tubing with a largish diameter around 3/4 inch (20 mm.),
and with current around or a little over 100 milliamps. Most of these tubes
were long and U-shaped.

Nowadays, there are miniature cold cathode fluorescent lamps. Most of these
are 3 to 6.4 mm. (1/8 to 1/4 inch) in diameter and usually take a current
around 5 milliamps (sometimes as low as 2.5 mA). These are mostly used as
backlights for LCD screens in laptop computers and the like. (NOTE: Some
laptops use smaller standard and/or compact fluorescent lamps and some use
electroluminescent panels.) A few miniature cold cathode fluorescent lamps
are used in other applications such as solar powered lawn lights.

There are a few blacklight versions of miniature cold cathode fluorescent
lamps.

A major manufacturer of miniature cold cathode fluorescent lamps is
JKL Lamps.

There are some incandescent bulbs such as some flashlight bulbs with xenon
in them. Some halogen bulbs including some automotive headlight bulbs have
xenon in them also. But these are all incandescent lamps and not arc lamps.
There is an advantage, usually minor, in using xenon instead of the usual
argon-nitrogen mixture or plain argon (or sometimes krypton) in these.

There are HID (electric arc) automotive headlight bulbs, and they do
contain xenon but these are a kind of metal halide lamp. The xenon is an
active ingredient used to produce some usable white light until the bulb
warms up enough for other active ingredients to evaporate.

UHP lamps are Ultra High Pressure mercury vapor lamps, similar to HBO short arc
mercury vapor lamps. UHP lamps differ slightly from HBO lamps, by being in a
narrower range of wattages (lower ones), mostly having a somewhat higher voltage
drop than same-wattage HBO lamps at least in part by having pressure a little
higher than usual of HBO lamps, and by being designed for a recent new modern
application - digital projectors.

The visible spectrum of a typical UHP lamp is mostly a smooth continuous
spectrum, with three somewhat brighter bands centered on the 436 nm (violetish
blue), 546 nm (slightly yellowish green), and the 577/579 nm (yellow) main
visible wavelengths of mercury vapor. The color rendering effect is close
to that of an old-tech "daylight" fluorescent lamp, although in an LCD
digital projector (where a trichromatic RGB light source works better than
even a truly daylight-spectrum light source), the color rendering effect
is a little noticeably dim for red and reddish colors.